1. Field of the Invention
This invention relates to a device which, by automatically adjusting the position of the shed vertex cloth fell in said loom during the transient states following loom stoppages in such a manner as to maintain the reed beat-up intensity always equal to its normal working intensity, enables a defect-free fabric to be woven continuously.
2. Description of the Prior Art
As is well known, because of its inertia the loom, after each stoppage, achieves its working speed only after a transient state during which the weft is beaten up by the reed at an intensity less than the working intensity, with the result that the weft does not finish up in the same position as the wefts subsequently beaten up at working intensity, so that a defect visible to a greater or lesser extent depending on the difference in beat-up intensity appears in the fabric due to differing weft density. Said defect, which up to a short time ago was substantially unnoticeable and hence was not a problem given the relatively low speed of the looms used, because of which the intensity with which the first weft after loom stoppage was beaten up was substantially very close to working intensity, has now become visible and hence unacceptable, because of the high speed of modern looms.
To obviate this drawback, it has been sought to restart the loom as rapidly as possible so as to quickly attain working speed and hence beat-up the first weft after loom stoppage with an intensity as close as possible to the working intensity.
In practice, the coil of the electromagnet which attracts the friction disc is overpowered for the entire transient state period so as to nullify disc slippage.
This known method has considerably lessened the problem of fabric defects during transient states after loom stoppages but has not completely solved it, because in addition to the fact that the weft is still beaten up at an intensity slightly different from the working intensity, the vertex of the shed forming the fabric generally moves during loom stoppage because of the plastic deformation of the warp and fabric, and in addition the inevitable friction produced during the movement of the fabric itself results in a variation in the position of the vertex of said shed, so that the wefts are beaten up during transient states in different positions than during normal working.
Attempts have been made to overcome these latter drawbacks involving variation in the position of the shed vertex by locking the take-up roller and/or beam in position during the transient states.
This has considerably limited said vertex position variation but has not completely nullified it.
Hence notwithstanding the various methods used up to the present time, there still remains the drawback that during transient states the weft is not beaten up in the same position as during normal working because there is always a more or less accentuated shift in the position of the shed vertex.